1. Field of the Invention
The present invention is generally related to electrostatic discharge (ESD) safe ceramic (sometimes “ESD dissipative ceramic,” or “ESD ceramic”) compositions, components, and methods for forming same, and in particular is drawn to ESD safe ceramic components based upon a zirconia toughened alumina (ZTA) material.
2. Description of the Related Art
In the area of electrostatic discharge (ESD) safe ceramics, various compositions have been developed in an attempt to bring together important electrical, thermal and mechanical properties of materials for end use applications that are sensitive to electrostatic discharge.
Most notably, zirconia-based materials have been investigated for use in environments sensitive to ESD. Generally speaking, zirconia is transformation-toughened, containing a stabilizer to partially stabilize the zirconia in a tetragonal crystal structure. Among various toughened zirconias, tetragonal partially stabilized zirconia has balanced properties including high strength, fracture toughness, corrosion resistance, and excellent machinability. For these reasons, tetragonal partially stabilized zirconia has been used for metal forming tools, blades/knifes, handling tools (e.g., tweezers), and optical fiber connectors (ferrules), and have found recent use replacing tool steels, stainless steels, special alloys and cemented tungsten carbides (WC).
However, because toughened alumina is an electrical insulator having a volume resistivity greater than 1012 Ohm-cm, it is not particularly suitable for ESD safe applications. In this regard, a technical background relating to the need for improved ESD materials can be found by reviewing publicly available information from the ESD association. See www.esda.org., for example.
Recently, a need has arisen in the art for ESD dissipative or ESD safe components which not only have desirable ESD properties, but which also have desirable thermal expansion properties, flexural strength, toughness, hardness, wear resistance, and other properties. Some of the demand is motivated by the need to find ESD safe materials which find use in certain demanding commercial applications such as bonding tips for microelectronic use, handling tools for magneto-resistive head fabrication, bonding capillaries, and similar applications. In this regard, zirconia based ceramics, including zirconia based ESD ceramics have been found to lack sufficient rigidity, stiffness, wear resistance, and abrasion resistance for certain demanding tool applications. In addition, it has also been found that zirconia based ESD ceramics may not have suitable thermal conductivity and thermal expansion properties.
Accordingly, based on the foregoing, the present inventors have recognized a need in the art for improved materials finding particular use in demanding applications, which require unique mechanical, structural and electrical properties.